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  What are the main circuits in the Thermal Power Plant? Answer: Thermal Power plant consists of four main circuits, they are:   Feed water and steam flow circuit Coal and ash circuit Air and gas circuit Cooling water circuit Steam power plant works on which cycle? Answer: Steam power plant works on the principle of Rankine Cycle What is the Thermal efficiency of steam power plant? Answer: Thermal efficiency of steam power plant is defined as the ratio of heat equivalent of mechanical energy transmitted to the turbine shaft to the heat of combustion. Generally Thermal efficiency of the steam power plant will be in the range of 30-35% What is the overall efficiency of the Thermal Power Plant or Steam Power Plant? Answer: Overall efficiency of the system is defined as the ratio of heat equivalent of electrical output to the heat of combustion. Generally Overall efficiency of the steam plant will always be less than the thermal efficiency of the steam plant, it will be of the order of 29-33% Overall efficiency of steam plant is determined by multiplying the thermal efficiency of the plant with efficiency of the generator (electrical efficiency) Why the Thermal efficiency of the steam power plant is quite low? Answer: In Steam power station, more than 50% of the total heat of combustion is lost as heat rejected to the condenser and the loss is unavoidable as the heat energy cannot be converted in to mechanical energy with out a drop in temperature. Steam in the condenser is at lowest temperature. This is the reason that the thermal efficiency of the power plant is quite low. On what factors efficiency (thermal) of the steam plant depends? Answer: Efficiency of the thermal plant depends on three factors, they are Pressure of steam entering the turbine Temperature of the steam entering the turbine   Pressure in the condenser Thermal efficiency increases with increase in temperature and pressure of the steam entering the turbine. For this reason high temperature and pressure are used. Thermal efficiency is effectively increased by decreasing the pressure in the condenser, so pressure in the condenser is kept as low as possible. Thermal efficiency also increases by reheating the steam between turbine stages What are the major electric systems in Thermal Power Plant? Answer: Major electrical equipment in thermal power plant are Turbine Generator Exciter System Generator Protection System Generator Transformer HT/LT switch gear Electrical Switch-yard What are the different Generator Protections employed in Thermal Power Plants? Answer: Faults in the windings, Over load protection, Over heating of windings or bearings, Over speed protection, Loss of Excitation protection, Motoring operation protection, Inadvertent energisation, single phase or unbalanced current protection, out of step operation protection, sub-synchronous oscillations protection and earth fault protection How Generator Transformer is cooled in Thermal Power Plant? Answer: MVA power rating of the Generator Transformer will be equal to the alternator. Hence lot of heat will be generated while generator transformer is under operation. Oil Forced Air Forced (OFAF) type of cooling is employed for generator transformer What are different types of circuit breakers employed in thermal power plant? Answer: For low voltage operation 415/220V vacuum circuit breakers or air break circuit breakers are employed. For voltage ratings about 6.6kV and beyond SF6 circuit breakers are employed. What type of cooling is provided for Generator in power plant?  Answer: Hydrogen gas cooling is employed for large size generators because of better heat carrying ability of the hydrogen. Hydrogen cooling is provided for rotors and core of the generator. Water cooling is provided for the stator of the alternator.  Thermal efficiency of Steam Power Plant: In steam power plant overall efficiency will be in the order of about 30%. In case of modern thermal power plats where super critical parameters (pressure and temperature) are employed and by employing number heat savig devices the power plant efficiency will be raised to around 40%. Quality of the coal also plays significant role in improving the efficiency of the Thermal Plant.   Some the losses occurring i the steam power plants are: Loss at Boiler - 15% Loss at the Turbo-Generator Heat Rejection to the condenser - 55% Alternator loss - 1% From above mentioned figures we understand that more than 50% of total heat combustion is lost as heat rejected to the condenser. This loss cannot be avoided as heat energy cannot be converted into mechanical energy without (some heat rejected) drop in temperature (From the second law of thermodynamics-A fraction of heat can only be converted to mechanical work and remaining heat must be rejected). Steam in the condenser is at lowest temperature. Thermal efficiency of the power plant mainly depends on three factors. a) Pressure of the steam entering the turbine b) Temperature of the steam entering the turbine c) Pressure in the condenser Thermal efficiency of the plant can be improved by increasing the temperature and pressure of the steam. For this reason high temperature and pressure is used and also thermal efficiency is improved by decreasing the pressure in the condenser Also efficiency can be improved by reheating the steam between the turbine stages Turbine Generator Hydrogen Seal System  For large generators in power plants hydrogen cooling is provided for efficient heat transfer and electrical properties are superior to non explosive gases. High purity hydrogen will not support combustion. However when hydrogen mixed with air to the level of 95% purity, it is explosive in nature. Therefore a sealing system must be provided to prevent the hydrogen gas from escaping from the generator casing. This is done by maintaining pressure on an oil seal around the generator shaft. As long as the oil pressure is greater than the hydrogen gas pressure, a seal will be formed confining the gas inside the generator and preventing leakage to the areas outside the casing. For a generating unit the seal oil motors would consists of the following: AC main seal oil pump (MSOP) DC emergency seal oil pump (ESOP) AC motor driven vacuum pump The main seal oil pump is used normally and is backed up by the dc emergency seal oil pump, which is fed from the station battery. These pumps circulate oil through the seals while the vacuum pump removes the hydrogen from the oil in the hydrogen drain tanks. Some vendors will furnish two seal oil pumps instead of one. These pumps, one for each side of the seal, are called the air side and hydrogen side seal oil pumps ………………..  
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